It is well established in energy circles, that laboratory buildings are among the most energy intensive. A sufficient contributor to this reputation is the energy used in the operation of fume hoods, a ubiquitous and seemingly indispensable piece of scientific apartatus. Fume hoods insure that chemical and biological experiments using volatile or otherwise dangerous chemicals are contained in a well ventilated space designed specifically to protect the researcher.
Past efforts to secure fume hoods not in use has led to near disasters. Some positive flow of air is always required to insure the safety of the laboratory.
A system has now been discovered that insures safe positive ventilation while reducing air flow during off hours and the energy savings are considerable.
Broadly speaking, limit switches sense the sash position and vary the air flow between a high volume flow when the sash is in an open position, and a low volume flow when the sash is in a closed position. Sensors also determine if the velocity through the hood is proper and, if not, actuate an alarm. A light sensor measures the ambient light in the room. If the light is too low and the high volume fan is on an alarm is actuated generally indicating the sash is open after hours. The low volume fan operates continously. The system, in total, ensures that when not in use the sash will be closed allowing the minimal air flow; and if there is a safty problem i.e., no negative air flow an alarm is actuated.